Focal plane arrays and other such imaging devices are generally associated with a readout circuit. The imaging array is divided up into columns of detectors, with each detector representing a pixel of the array. The detectors may be, for example, quantum well infrared photodetectors (QWIPs) or charge coupled devices (CCDs) or microbolometers. Each of the detectors in any one column of the array is associated with a common readout circuit. The array and the readout circuit are typically implemented on separate chips.
In operation, light (e.g., infrared) impinges on the array, thereby causing each of the illuminated pixels of the array to generate an analog detection signal. Each analog detection signal is then sent to a corresponding readout circuit, where it is processed (e.g., integrated, amplified, filtered, and converted to its digital equivalent). The digitized pixel data can then be processed as necessary (e.g., image formation and artifact removal), as is conventionally done. The image processing circuitry is usually implemented on a separate chip.
A common problem with conventional array and readout circuit designs is related to the common readout circuitry associated with any one column of detectors. In particular, a functional defect in the common readout circuitry effectively eliminates data from every detector or pixel in the column associated with that common readout circuitry. Although the overall array can still function with such column outages, image data from the detected scene is lost, thereby degrading image quality. In addition, certain imaging applications in the military and commercial sectors (e.g., targeting and surveillance) may be intolerant of such data loss.
What is needed, therefore, is an imaging system that is less prone to data loss resulting from defective readout circuitry.